1. Field of the Invention
This invention relates to a matrix type display device employing a TFT (Thin Film Transistor) array substrate, and more particularly to a liquid crystal display device which is improved by a reduced possibility of wiring breakage defects and a higher yield in manufacturing the device with a larger area and a higher resolution.
2. Description of the Prior Art
FIGS. 1 and 2 each illustrate a TFT array substrate constituting a conventional liquid crystal display device of the above-mentioned type. FIG. 1 is a partial plan view of the TFT array substrate produced by a conventional manufacturing method, while FIG. 2 is a enlarged partial sectional view taken along line II--II of FIG. 1.
In the figures, numeral 1 denotes a transparent insulating substrate, 2 gate electrode wiring, 3 a gate insulation film, 4 a semiconductor film, 5 a source electrode wiring, 6 a drain electrode, and 7 denotes a display electrode.
The method of manufacturing the TFT array substrate according to the prior art will now be explained below while referring to FIGS. 1 and 2. First, a transparent conductive film of indium tin oxide (hereinafter abbreviated to "ITO") or the like is deposited on a polished and cleaned surface of a transparent insulating substrate 1 of glass or the like by a sputtering process, an EB (Electron Beam) vapor deposition process or the like, followed by a photo-etching process or the like to form the pattern of display electrodes 7 desired.
Next, a film of a metal such as Cr, Ta, Al, etc. or an alloy thereof is deposited by a sputtering process, an EB vapor deposition process or the like, followed by a photo-etching process to form the pattern of gate electrode wiring 2 desired.
Then, a film of dielectric such as SiN and SiO.sub.2 as a gate insulation film 3 and a film of amorphous silicon (hereinafter abbreviated to "a-Si") or polysilicon (hereinafter abbreviated to "P-Si") as a semiconductor film 4 are consecutively deposited by a plasma CVD process or the like. The upper semiconductor film 4 is patterned by a photo-etching process or the like, and the lower gate insulation film 3 is patterned by a similar process.
Finally, a film of a metal such as Al or an alloy thereof is deposited by a sputtering process, an EB vapor deposition process or the like, followed by a photo-etching process or the like to form source electrode wiring 5 and drain electrodes 6. Thus, the TFT array substrate is completed.
The method of producing the TFT array substrate constituting the liquid crystal display device according to the prior art employs the above-mentioned steps. There is the problem that during the repeated film-forming and patterning steps before the completion of the source electrode wiring 5, foreign matter such as dust may be deposited on the substrate, or defects may be present in a resist used for the photo-etching step for forming the source electrode wiring 5, resulting in breakage of the source electrode wiring.
Particularly when the substrate becomes larger, with an attendant increase in the number of the conductors, or density is increased with an attendant reduction in the width of the wiring, the possibility of the breakage of source electrode wirings is increased sharply.
Accordingly, the TFT array substrate and the liquid crystal display device as the matrix type display device produced by the above-mentioned method have the problems of poor performance and an extremely low yield of the product.